There are three manners in which support struts for a walking machine, in particular for a concrete pump vehicle work, in a first of which front struts are extensible with one crossing the other, and rear struts swing rearward or in a H-form; in a second of which both front and rear struts swing rearward to be retracted back; and in a third of which, front struts swing forward to be retracted back and rear struts swing rearward to be retracted back. All these support struts are pivotable or extensible with respect to an axis of a chassis, and have a vertical supporting cylinder at an end of the strut so as to allow the walking machine to obtain a stable working condition in operation.
Both EP0357988 and DE3124029 disclose a motorized concrete pump vehicle having crossed extensible front struts, in which the concrete pump vehicle is provided with a frame with two or more axles, the frame being provided with a material distributing rod rotatable about a vertical axle, the material distributing rod being mounted on a rod seat close to a front axle, and two forward-facing extensible struts arranged diagonally with one crossing the other, the two extensible struts arranged with one crossing the other being at different heights, the front struts and extensible tubes being arranged on a holding seat fixedly attached to the rod seat. EP0357988 discloses a pump vehicle provided with two extensible rear struts in a rear end region of the extensible tubes of the front struts, said rear struts being mounted such that they are rotatable around a vertical axle, they rotate rearward from a driving position thereof in parallel with the frame and enter their positions arranged rearward outward and diagonally. DE3124029 discloses a pump vehicle provided with H-form rear struts in a rear end region of the extensible tubes of the front struts, sheaths of said rear struts being mounted parallel to a wheel axle of a chassis, the rear struts being extensible along their sheaths.
DE4203820 discloses a concrete support strut of a swinging type, in which the struts are attached to pins of a swivel base, with a swinging cylinder connected between the swivel base and the swinging struts. When the concrete pump vehicle pumps concrete to a casting point, the front struts revolve outward about the pins to a supportable position. When the pump vehicle is in a running status, the struts retract inward to the two sides of the pump vehicle. Such a device has the disadvantage of not allowing an operation on a narrow construction site due to its structural dimensions.
U.S. Pat. No. 6,840,540 discloses a forward swinging support strut for mobile working machines. The support strut has a strut body that can be pivoted around a vertical pivoting axis on a chassis, a telescopic part that is telescopically displaceable relative to the strut body, a double-acting hydraulic cylinder that extends through the strut body and the telescopic part, and a support part provided at the outboard end of the telescopic part, the extensible cylinder being connected at its respective ends to securing points in the area of opposing ends of the strut body and the telescopic part, and the vertical pivot axis being defined by divided bearings located on the strut body spaced axially a distance from the cylinder inboard securing point in the direction of the foot part, and so positioned that said vertical axis transects the axis of displacement of the hydraulic cylinder.
The technical solutions as disclosed in the above-mentioned patent documents contain technical problems as below.
For a walking vehicle with a swinging support strut, as the swinging strut requires a large space to be extended due to its structural dimensions, it cannot operate on a narrow construction site. And in an embodiment of EP0357988, as the axes of the front struts and the rear struts are connected with an angle, stresses coming from the material distributing rod and transferred via the rod seat should be applied to the rear struts along the entire length of the vehicle, which requires a great effort in the design of the vehicle frame, thereby raising the manufacturing cost of the product.
When taking a H-form rearward strut, as a length along which stresses coming from the material distributing rod are transferred via the rod seat and the vehicle frame to the rear struts is increased, it requires to enlarge a structure and to increase a weight of the vehicle frame so as to ensure that the vehicle frame has sufficient rigidity, thereby raising the design and manufacturing costs of the product.
When taking a forward swinging strut, as it requires that a hydraulic cylinder is mounted to each strut side to carry out the process of the struts pivoting around the pins, the structural design is more complicated and the cost is higher, and moreover, it requires relatively more time changing the strut from a retracted condition into a working condition, which reduces efficiency in operation.
Thus, an object of the present invention is to provide an improved extensible support device and a concrete pump vehicle using such a support device which overcomes the shortcomings existing with support devices in the prior art. The device according to the present invention, which has a simple structure, is extensible within a short time and can be used in operation on a narrow construction site. A support device used for a walking machine, such as a concrete pump vehicle, which has a more compact structure and makes full use of a space of the support device, allows the forces borne by the left and right struts to be more balanced so as to improve the stability of the entire vehicle in operation.